The invention the subject of the present application relates to paper wrappers for wrapping smoking materials of smoking material rods of smoking articles. Hereinafter such wrappers are referred to as cigarette papers.
It has previously been proposed to provide cigarette paper comprising magnesium oxide, the purpose of such paper being to effect, in comparison with a conventional cigarette paper, a reduction in visible sidestream smoke. This cigarette paper has, however, proved to be less than fully satisfactory. Thus, for example, cigarettes incorporating the prior proposed sidestream-smoke reducing paper were noticed by smokers to exhibit a mainstream smoke off-taste and poor ash formation.
It is an object of the subject invention to provide an improved sidestream-smoke reducing cigarette paper.
It is a further object of the subject invention to provide an improved low sidestream smoke cigarette or similar low sidestream smoke smoking article.
The subject invention provides cigarette paper comprising a total filler content of about twenty per cent by weight, or less, a proportion at least of the filler being a filler capable of effecting visible sidestream reduction, the weight of the paper being about thirty grams per square meter or more.
The subject invention also provides a smoking article comprising a smoking material rod, which rod comprises smoking material and a paper wrapper circumscribing said smoking material, and said paper of said paper wrapper comprising a total filler content of about twenty per cent by weight or less, a proportion at least of the filler being a filler capable of effecting a reduction in visible sidestream, the weight of said paper being about thirty grams per square meter or more.
Preferably, the filler which effects a reduction in visible sidestream is magnesium oxide and/or magnesium hydroxide or high surface area chalk or mixtures thereof. Magnesium oxide utilised for the purposes of the present invention is preferably a reactive grade of magnesium oxide.
In addition to the visible sidestream reducing filler, the filler may comprise conventional chalk. If conventional chalk is present, it is preferably present in a range of about twelve per cent by weight of the paper to about three per cent by weight of the paper, and more preferably does not consitute more than about ten per cent by weight of the paper. The minimum level of total filler present in the paper may be about four percent by weight of the paper. The visible sidestream reducing filler may be the sole filler in the paper.
Suitably, the visible sidestream reducing filler content is in a range of about four per cent to about eighteen per cent by weight, but is advantageously at or above about seven per cent by weight. Where the visible sidestream reducing filler is magnesium oxide and/or magnesium hydroxide, said filler is present in a range of about 1.5 grams to about 5.3 grams per square meter of the paper. Where the visible sidestream reducing filler is high surface area chalk, said filler is present in a range of about 3.8 to about 5.9 grams per square meter.
The inherent permeability i.e. that due to viscous flow, of the paper is advantageously about ten Coresta units or less. The permeability is suitably about seven Coresta units or less and is more suitably about five Coresta units or less.
The air permeability of a paper expressed in Coresta Units is the amount of air in cubic centimeters, which passes through one square centimeter of the paper in one minute at a constant pressure difference of 1.0 kilopascal.
Inherently porous cigarette paper consists of an interlocking network of fibres, which fibres are usually substantially wholly or mainly cellulose fibres, interspersed with particles of a filler, calcium carbonate for example. Openings in the fibre/filler matrix are of the order of 1 um wide, which dimension is small compared with the thickness of the paper (usually 20 to 50 um) and the flow of air through such openings is governed by viscous forces. However, when paper is perforated after the paper making process, the perforations are relatively large, usually having width dimensions of the same order of magnitude as the paper thickness, and the flow of air through such perforations is governed by inertial-forces.
It is thus to be observed that when the permeability of a perforated paper is determined in accordance with the Coresta permeability determination method, the permeability value obtained will comprise the sum of the permeability due to viscous flow through the openings inherent from the paper making process and the permeability due to inertial flow through the perforations. A paper will also exhibit the same two permeability components if, although not perforated, the paper comprises, in addition to the small, viscous flow holes, larger inertial flow holes, which latter holes may be referred to as pinholes. Paper of this last mentioned construction may result, for example, from a defective paper making technique.
The total air flow through a paper may be expressed as:
Q=ZAP+Zxe2x80x2A(P)n
where
Q is the air flow (cm3 minxe2x88x921)
A is the area of paper (cm2) exposed to the flowing air
P is the pressure difference across the paper (kilopascals)
Z is the permeability of the paper due to viscous flow through the openings inherent from the paper making process in Coresta Units (cm minxe2x88x921 kilopascalxe2x88x921)
Zxe2x80x2 is the permeability of the paper due to inertial flow through perforations and/or pinholes (cm minxe2x88x921 kilopascalxe2x88x921) and
n is a constant for a given set of perforation holes or pinholes, where 0.5 less than n less than 1.0, the exact value of n depending on the size of the perforations or pinholes.
The total permeability of a paper comprising perforations and/or pinholes is (Z+Zxe2x80x2) and the relative values of Z and Zxe2x80x2 for a given such paper can be obtained by measuring the flow of air through the paper at a series of pressure differences across the paper and numerically regressing the Q/P data in the above equation using a value of n in accordance with the mean size of the perforations/pinholes in the paper.
It is to be understood that the value of 10 Coresta units recited above in relation to the wrappers of smoking articles according to the subject invention refers to the permeability of the wrappers due to viscous flow. It will thus be appreciated that it is conceivable for a wrapper of a smoking article according to the subject invention to have a total permeability, i.e. the permeability determined using the Coresta permeability determination method, exceeding 10 Coresta units should the wrapper comprise perforations and/or pinholes.
Conveniently, the maximum weight of total filler is about 8 grams per square meter. The minimum weight of total filler in the paper may be about 1.5 grams per square meter. The total filler may preferably be less than 7.0 grams per square mater and may advantageously be within the range of about 4.0 grams per square meter to about 6.5 grams per square meter.
The weight of paper is suitably about thirty five grams per square meter or more, and more suitably about forty grams per square meter or more.
By preference papers according to the subject invention comprise a burn additive in a range of about two to about ten per cent by weight. Those skilled in cigarette paper technology will readily be able to identify burn additives. Additives found to be effective for the purpose of the subject invention include sodium acetate, tri-potassium citrate, potassium di-hydrogen orthophosphate and potassium tartrate. The salts of the burn additives may be alkaline or acidic in aqueous solution. The burn additives may be either burn rate promoters or burn rate retardants generally in a range of from about 0 to about 2.3 grams per square meter of cigarette paper.
The smoking material of a smoking article in accordance with the subject invention may comprise a proportion of expanded tobacco. The expanded tobacco suitably has a bulk density in a range of 100 mg cmxe2x88x923 to 175 mg cmxe2x88x923. The proportion of the smoking material accounted for by expanded tobacco may be at least about ten per cent by weight and may suitably be at least about twenty per cent by weight, more suitably at least about thirty per cent by weight, and even more suitably at least about forty per cent by weight.
The length of smoking material rods of smoking articles in accordance with the subject invention is preferably not less than 45 mm and is advantageously at least 55 mm. The smoking material rods are preferably of uniform cross-sectional shape and dimensions throughout the lengths thereof. If, as is commonly the case with cigarettes and like smoking articles, a smoking material rod of a smoking article in accordance with the subject invention is of a uniform circular cross-section, the circumference of the rod may be in a range of 10 mm to 30 mm. Whereas significant and commercially useful sidestream smoke reduction advantages are to be obtained from smoking articles in accordance with the present invention when the rod circumference is 25xc2x15 mm, further advantage is to be had when the rod circumference is below the 25xc2x15 mm range down to 10 mm. Preferably, the rod circumference of smoking articles according to the subject invention is not less than 12.5 mm.
When smoked under standard machine smoking conditions, smoking articles in accordance with the subject invention advantageously provide not less than five puffs and more preferably not less than six puffs.
Preferably, smoking articles in accordance with the subject invention comprise filter or mouthpiece means attached to the smoking material rod at one end thereof.
Smoking articles in accordance with the subject invention may incorporate ventilation means.
It is also to be understood that smoking articles according to the subject invention may be wrapped in a wrap which may comprise one or more overlying or underlying wrapper sheet materials.